I would liken it to the current paths between two electrodes placed in ground, these form paths identical to what happens when you place iron filings on a paper between two opposite poles of a magnet; they are curved between each pole (polarity) in ever longer and increasing radial length. Since the full 120V is across the furthest two points within the radio/whatever then it should be a matter of ratio of distance over length of body exposed. Then again the more salt in the water, the lower the resistance across the two points the less risk to a higher resistance human body? Heck! maybe I should just try it out in the Jacuzzi (with a battery radio I think!).